1. Field of the Invention
The present invention relates to a variable valve lift apparatus. More particularly, the present invention relates to a variable valve lift apparatus which have a control portion for controlling valve lift within a camshaft.
2. Description of Related Art
An internal combustion engine generates power by burning fuel in a combustion chamber in air media drawn into the chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
An optimal operation of the intake valves and the exhaust valves depends on a rotation speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on the rotation speed of the engine. In order to achieve such an optimal valve operation depending on the rotation speed of the engine, various researches has been undertaken. For example, research has been undertaken for a variable tappet that enables different lifts depending on an engine speed.
However, a conventional variable valve lift apparatus needs a space for a control portion for controlling valve lift, so that entire volume of an engine has to be increased.
And also, if a manufacturing line using a general valve lift apparatus is changed to a manufacturing line using a conventional variable valve lift apparatus, a valve train has to be changed so that production cost is increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.